1. Technical Field of the Invention
The present invention relates to a mobile telecommunications network and, in particular, to a method and system for determining the current geographic location of a mobile station.
2. Description of Related Art
Within a fixed or wireline telecommunications network, a geographic location associated with a particular wireline subscriber has always been determinable. A physical circuit connection between a telecommunications exchange and a telecommunications terminal connected thereto readily identifies the exact location of the associated wireline subscriber. As a result, in response to a need to locate a wireline subscriber, the serving telecommunications exchange merely has to perform a line trace along the circuit connections to determine the location of the calling party subscriber. Alternatively, the serving telecommunications exchange can determine the directory number associated with the calling party subscriber. The ascertained directory number is physically associated with a particular access line (telephone line) and can then be translated into an exact geographic location.
Unlike the wireline telecommunications system, locating a mobile subscriber within a mobile telecommunications network is much more difficult. By effectuating communication by way of a radio link, a mobile station is able to travel throughout the geographic area covered by a mobile telecommunications network and be served by any one of the associated mobile telecommunications exchanges, such as mobile switching centers (MSC), and/or base station controller (BSC). As a result, it is no longer sufficient to merely determine the associated directory number to ascertain the current location of the mobile station. Furthermore, no wireline circuit connection is available for purposes of ascertaining location data.
A number of methods and mechanisms have been introduced to determine the geographic location of a mobile station. Such methods include triangulation or arcuation methods utilizing the signal strength received from three or more neighboring cells or base transceiver stations (BTSs). Other mechanisms include the Global Positioning System (GPS) utilizing multiple satellites and associated signals to ascertain the current geo-coordinates. Other more crude methods include merely determining the current cell or coverage area associated with the mobile station and identifying the approximate geographic area associated thereof. A number of other mechanisms and devices are already well known within the mobile telecommunications field for locating a mobile station.
With the popularity of mobile stations and a drastic increase in the number of mobile subscriptions in recent years, mobile service providers and/or associated government agencies want to be able to more accurately locate mobile stations. For example, the Federal Communications Commission (FCC) has released a mandate requiring all mobile service providers in the United States to be able to pin-point a mobile station with an accuracy of one hundred fifty (150) meters in case of an emergency call (911 call). Such a location determination then enables a Public Safety Answer Point (PSAP) to provide effective emergency assistance to mobile subscribers in need of help.
Unfortunately, all of the conventionally known location methods or mechanisms are either too inaccurate or too sail expensive. For example, the GPS location system requires each mobile station to be equipped with an expensive GPS locator. The triangulation and other cell strength methods, on the other hand, are too inaccurate to provide satisfactory location data. Furthermore, since each cell may cover a few miles in radius, identifying the serving cell is similarly inadequate to accurately locate the mobile station. As a result, in order to more accurately determine the geographic location of a mobile station without requiring the mobile station to be equipped with an additional device, cell coverage areas need to be reduced. By reducing each cell coverage area and increasing the number of BTSs, a more accurate calculation of mobile station location can be performed. Such dense cell planning is, however, expensive and impractical.
Accordingly, there is a need for a mechanism to provide an economical, yet accurate, mobile station location system.